The present invention relates generally to laser communication systems. More specifically, but without limitation thereto, the present invention relates to a laser communications link between aircraft and underwater platforms.
The problem of communicating with unmanned undersea vehicles (UUV""s) has received much attention in the prior art. UUV""s may surface and communicate by radio in the same manner as surface vessels, but this manner of communication suffers from disadvantages such as interruption of a mission, increased vulnerability to weather and threat activity on the surface, and lack of communication when surfacing is not permissible.
Radio communication systems have been devised that permit some degree of communication with submerged vehicles and platforms such as UUV""s, however these are sharply limited in their application because of attenuation of RF signals in water and also because they provide a means whereby eavesdroppers may locate and identify the transmissions made from the submerged vehicle.
Surface buoys connected by an electrical cable to a UUV have been used to permit the maintenance of a relatively safe depth, but these are also susceptible to surface detection.
Communication with a friendly aircraft over the area occupied by a submerged vehicle or with an orbiting satellite is possible using the highly directive properties of modulated light beams. The energy of such beams does not generally disperse beyond the immediate location, thereby improving the security of the communications link. A laser beam also has the capability of penetrating sea water to some degree, particularly in the blue-green wavelengths. However, the high visibility of a blue-green laser from the air compromises the security of the submerged vehicle.
A need therefore continues to exist for a laser communications device for submerged platforms with aircraft and orbiting satellites.
The present invention is directed to overcoming the problems described above, and may provide further related advantages. No embodiment of the present invention described herein shall preclude other embodiments or advantages that may exist or become obvious to those skilled in the art.
A laser communications link of the present invention provides a downlink laser beam having a wavelength suitable for transmission through water transmitted from an aircraft or satellite to a submerged vehicle. An uplink laser beam having a wavelength that is visually undetectable is conducted through the water from the submerged vehicle by an optical fiber and radiated from the optical fiber at the surface of the water to the aircraft or satellite.
An advantage of the laser communications link of the present invention is that communications with a submerged vehicle may be made with an aircraft or a satellite.
Another advantage is that the transmission from the submerged vehicle has a wavelength in the near infra-red that makes detection visually or by broadband detectors unlikely.
Still another advantage is that the transmission from the submerged vehicle only requires a few watts of electrical power.
Yet another advantage is that because the transmission from the submerged vehicle is conducted by a fiber optic cable, the transmission is not scattered by the water.
Another advantage is that data communication rates from 100 MHZ to several GHz are achievable.
The features and advantages summarized above in addition to other aspects of the present invention will become more apparent from the description, presented in conjunction with the following drawing.